S1226
Clinical - Urology
ESTRO 2026
from a multicentric collaboration. Material/Methods: We included men with prostate cancer stage cT4N0- 1M0 treated with definitive external beam radiotherapy (EBRT) with androgen deprivation therapy (ADT) at 14 centres in India. Those with distant metastases, treated palliatively, or <1 year follow up were excluded. As per AJCC 8th edition, cT4 was defined as tumour fixed or invading external sphincter, rectum, levator muscles, and/or pelvic wall; and extent was classified as ‘gross’ (clinicoradiologically evident infiltration into adjacent structures) or ‘focal’ (lost or indistinct fat planes) on baseline imaging. Kaplan-Meier survival estimates of biochemical failure-free survival (BFFS), metastasis-free survival (MFS), and overall survival (OS) were compared for potentially prognostic factors using log rank and Cox proportional hazards methods. Results: A total of 351 eligible patients were included, with MRI T-staging for 69% patients (cT4 gross 52%, focal 48%) (Figure 1). Bladder, rectum and pelvic muscle infiltration was seen in 66%, 44%, and 13% respectively, with >1 site involved for 22% patients. Two-thirds of the patients (63%) had cN+ disease, and 69.5% had ISUP grade group (GG) 4-5 cancer. Staging PSMA-PETCT was available for 70% patients. Median duration of ADT was 30 months, and 16% received systemic intensification (ARPI/docetaxel). Median RT dose was 75 Gy EQD2 (IQR 75-78.8 Gy), with hypofractionation used in 70% (moderate 57%, SBRT 13%) patients. Almost all (90%) patients were treated with whole pelvic radiotherapy. Over a median follow- up of 50 months, 5-year BFFS, DMFS, and OS were 73.9%, 78.6%, and 88.7%, respectively. Among the 75 patients with disease recurrence, 91% underwent restaging with PSMA-PETCT, and a majority (85%) showed distant metastasis. Patients with gross cT4 disease showed significantly worse BFFS [HR 1.87 (95% CI 1.15-3.05), p=0.009] and MFS [HR 2.16 (1.25-3.74), p=0.004] than focal cT4 (Figure 2), remaining significant when adjusting for cN+ and GG.
multi-institutional cohorts is planned to confirm these preliminary findings and to integrate immune repertoire dynamics into clinical decision-making. References: 1 Ollivier L, Labbé M, Fradin D, Potiron V, Supiot S. Interaction Between Modern Radiotherapy and Immunotherapy for Metastatic Prostate Cancer. Front Oncol. 2021;11:744679.2 Kalina JL, Neilson DS, Comber AP, Rauw JM, Alexander AS, Vergidis J, et al. Immune Modulation by Androgen Deprivation and Radiation Therapy: Implications for Prostate Cancer Immunotherapy. Cancers (Basel). 2017 Jan 27;9(2):13. Keywords: oligometastatic, prostate cancer, T-cell receptor, Poster Discussion 2338 Definitive Radiotherapy for Stage T4 Non- Metastatic Prostate Cancer: Long-Term Outcomes from a multicentric collaboration Priyamvada Maitre 1 , Vasanthapriya Subramani 1 , Shikha Goyal 2 , David Simson 3 , Kushal Narang 4 , Indranil Mallick 5 , Renu Madan 2 , Jaskaran Singh Sethi 3 , Tejinder Kataria 4 , Moses Arunsingh 5 , Suman Mallik 6 , Tanweer Shahid 7 , Srinivas Chilukuri 8 , Jino Wilson 9 , Haridas Nair 10 , Bharath Chandra Gurram 11 , Nilesh Mahale 12,13 , A. N. Chinnachamy 14 , Trinanjan Basu 15 , Pallavi Singh 1 , Vedang Murthy 1 1 Radiation Oncology, Tata Memorial Centre, HBNI, Mumbai, India. 2 Radiation Oncology, Postgraduate Institute of Medical Education and Research, Chandigarh, India. 3 Radiation Oncology, RGCI, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India. 4 Radiation Oncology, Medanta Cancer Institute, Gurugram, India. 5 Radiation Oncology, Tata Medical Center, Kolkata, India. 6 Radiation Oncology, Narayana Superspeciality Hospital, Howrah, India. 7 Radiation Oncology, Apollo Multispeciality Hospital, Kolkata, India. 8 Radiation Oncology, Apollo Proton Cancer Centre, Chennai, India. 9 Radiation Oncology, Christian Medical College, Vellore, India. 10 Radiation Oncology, Amrita Institute of Medical Sciences, Kochi, India. 11 Radiation Oncology, Yashoda Cancer Institute, Hyderabad, India. 12 Radiation Oncology, Nirali Memorial Radiation Centre, Surat, India. 13 Radiation Oncology, Bharat Cancer Hospital, Surat, India. 14 Radiation Oncology, VN Cancer Centre, G. Kuppuswamy Naidu Memorial Hospital, Coimbatore, India. 15 Radiation Oncology, HCG Cancer Centre, Mumbai, India Purpose/Objective: Treatment for locally advanced prostate cancer of clinical stage T4 (cT4) has sparse evidence from clinical trials. We report clinical outcomes with definitive radiotherapy for cT4 non-metastatic prostate cancer
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